| Microwave Components Accuratus
serves a broad spectrum of microwave component suppliers. Ceramics are
widely used in the industry and Accuratus has been an active
participant since its founding. Power Tubes
Raw ceramic components and metallized hermetic ceramic components
suitable for brazed assembly are widely used in power tubes or vacuum
electron devices. Collector
ceramics require high dielectric strength and high thermal
conductivity. Significant heat is generated in the collector as the
kinetic energy of the electron stream is converted to heat. Getting the
heat out of the collector efficiently is critical to avoid melting or
severely damaging the collector assembly. Some of the ceramics here
serve as part of the vacuum envelope requiring hermeticity also. The
collector runs at several thousand volts below ground potential.
Electrical puncture of the ceramic can lead to catastrophic device
failure. Small discharges across the face of the ceramic can disrupt
the function of the device, rendering it unusable in an application.
Materials generally used in these applications are beryllium oxide and
aluminum nitride owing to their excellent thermal conductivity, vacuum
tightness and bulk and surface dielectric properties. Proper attention
to detail to prevent compromise of these critical material
characteristics is imperative for collector ceramics and is a hallmark
of Accuratus’ service to the industry. An
electron gun is mounted at the end of the tube opposite the collector.
Requirements here are generally less demanding however, the use of high
quality hermetic metallized ceramics is important. There is little heat
developed here and voltages are low. Aluminum oxide is generally the
material of choice. The need to stack several of these components with
critical inter-electrode spacing requires the precision machining
capability of Accuratus and the careful metallization of the components
by our industrial partners. RF
windows are produced for coaxial and waveguide inputs and outputs. The
windows must be hermetic and are normally brazed to the metal tube
envelope. Consistent dielectric properties and strongly adherent,
vacuum tight metallizing are critical. Typical materials of
construction are beryllium oxide and aluminum oxide although diamond
windows for extreme power output are produced. Loss
elements for various tube types are produced. Ring shaped components to
damp oscillations in klystron cavities are tailor made to customer
specification. Severs and loss buttons to control cavity Q, absorb
reflections from impedance discontinuities and drop interstage gain are
made in volume quantities. Porous aluminum oxide is used for low power,
less demanding applications. Higher power applications requiring
tightly defined loss characteristics and dielectric properties are
fabricated in customer supplied silicon carbide composite materials
typically with oxides such as magnesia, beryllia and alumina added to
develop specific properties. Where anisotropic material properties are
a concern, Accuratus maintains orientation with respect to raw material
pressing direction. Helix
traveling wave tubes are a special subclass of linear beam tubes
offering high gain over wide bandwidths. These tubes use electrically
long helical circuit elements mounted coaxially in a metal tube. The
electrical circuit is comprised of the helical metal ribbon, ceramic
supports and the metal outer tube all in a vacuum environment. Often,
many tubes are connected in parallel to generate higher power in
microwave systems thus requiring tight specifications on output power
and phase. Consistent dielectric properties and tight geometric
tolerances are necessary to assure the tube meets output
specifications. Low dielectric loss for good efficiency and low
dielectric constant to minimize loading of the circuit are important
material properties. The ceramic materials must also be capable of
transmitting significant heat from the helix. Typically, materials used
include beryllium oxide and boron nitride with aluminum oxide used on
some lower power low frequency legacy devices. Heatsinks
Heatsinks are used throughout the industry, particularly in the high
power segment, to transfer heat of both active and passive devices.
Important material properties include good to excellent thermal
conductivity and good to excellent dielectric properties. Materials in
common usage include aluminum oxide, beryllium oxide, boron nitride and
aluminum nitride. Common applications include:
— Resistor supports in high power combiners
— Dielectric supports for loads and terminations
— Transistor and diode bases
— Conduction cooled power tubes
— High power capacitor supports
— Coil forms in helical resonators
— High power dielectric resonator supports
— Substrates for hybrid microelectronics
— High frequency resistor cores Isolators and Combiners
Accuratus precision machines customer specified or customer supplied
ferrite and dielectric components. Tightly held tolerances for
components used in the GHz range are routinely and economically
produced for end users as well as for other suppliers to the industry. Tuning Elements
Precision components are produced for a number of variable capacitor
manufacturers. Low and moderate dielectric constant materials having
low loss are used; typically fused silica and aluminum oxide. Tight
tolerances and uniform material electrical properties are mandatory for
easy assembly and repeatable final product specifications. Customer
specified dielectric resonator pucks are also fabricated primarily for
the high power terrestrial microwave communications market. Specific
high dielectric constant components are produced to customer
specification. Electrically insulating, low loss supports for the
dielectrics are also produced. These may be required to minimize
perturbation of the electromagnetic field in the vicinity of the
dielectric. In high power applications they must transfer significant
quantities of heat out of the dielectric to avoid tuning drift, loss of
circuit Q and perhaps avoid catastrophic failure of the puck. See also: Materials > Aluminum Nitride
See also: Materials > Boron Nitride
See also: Materials > Fused Silica
See also: Materials > Macor | 
